jjsimp: They originally had a larger UI, but they got a lot of complaints and went the tiny route.
spindown: Small buttons are not a problem per se, but the UI doesn't seem to have a consistent style to it. It just looks chaotic and aesthetically unappealing, but that's just my opinion.
Actually looking closer at it, i still think its fine - whats not consistent?. Colour design of UI seems consistent with the overall colour theme of the game and smaller the better - see more of the action :)
The only concern i have is that the screenshot makes the gameplay section a bit 'grainy'.Definitely not clear but the UI is. Weird..